1. Field of the Invention
This invention pertains to heat exchangers and, more specifically, to a slide guide for cushioning tubes in a tube-type heat exchanger.
2. Description of the Prior Art
Heat exchanger manifolds such as those described in U.S. Pat. No. 3,689,972 to Mosier et al., in copending U.S. Pat. application Ser. No. 78,125 filed Sept. 24, 1979 to Rosman et al, and in copending U.S. Pat. application Ser. No. 095,287 filed Nov. 19, 1979 entitled "Yieldable Connector for Tube-Type Heat Exchanger" to Wagner, included herein by reference, have provided means of joining outer concentric tubes to a manifold. Rosman et al and Wagner likewise teach methods of joining inner tubes of a tube-in-tube heat exchanger to a manifold. However, the expansion and contraction of the heat exchanger tubes relative to the manifolds and mechanical stability of individual tubes has been a source of tube failure and heat transfer inefficiency.
FIG. 1 illustrates the conventional prior art for a heat exchanger tube penetration through a longitudinal periodically-spaced tube support sheet or flow baffle 10. In general, the sheet 10 thickness (t) is maintained thin for drilling, punching or stamping purposes. Also for cost and weight purposes the (t) value is minimized. In general practice, although undesirable, either edge 14 or 16 of the punched hole is a minimum radius element. A diametral clearance .delta. is provided also of a generally large value to ensure that the slight ovality, tube-to-tube diameter differences, and axial non-straightness are accepted during a low-cost easy assembly.
The heat exchanger operation is such that the heat exchange process is accompanied by fluid oscillations and noise occurring naturally as a result of frictional and aerodynamic dissipation both inside of and outside of the tube element 12. This oscillation results in the buffeting of the tube 12 in the sheet 10 radially and to some extent longitudinally with the center N as a nodal point. Moreover, particularly for designs which are thermally cycled, to a large extent the tubes 12 are translated each with respect to the tube sheet 10 to result in wear 18 as shown and eventual cracking 20 of tubes 12 through the wall with the subsequent very undesirable mixing of the working fluids and/or tube rupture. Moreover, the heat exchanger design practice is such that the required tube thickness is greater than that required for heat exchange and pressure stress to: (1) prevent failure due to fatigue and wear on thin wall tubes, (2) minimize bending and vibration due to fluid oscillation, and (3) add overall sturdiness to the tube sheets. The overall total cost of the added tube material both in terms of the initial capital cost and as well the operating cost to the diminished heat exchange (caused by the thick tube wall thermal resistance) is significant when the total number of tube heat exchangers on line operation in the world is considered.
In addition, the large financial and legal liability factors associated with heat exchangers particularly in hazardous potential operations such as nuclear or high-pressure steam or chemical plants, the reduction of heat exchanger tube failures is very desirable. Moreover, the heat exchanger down time and repair aspects of the heat exchanger component often result in substantial product loss.